Soviet forces pictured in Baku in May 1920.
April 28 1920, Baku–After the defeat of Denikin in the Kuban, the Reds turned their attentions south to the Transcaucasus. Their first target was the oil-rich Caspian port of Baku, the capital of Azerbaijan. The Bolsheviks had the most support there, having led the Baku Commune briefly in the summer of 1918 before the Turkish advance on the city. After the end of the war, the British returned to replace the Turks, but only remained until August 1919.
In late April, Bolsheviks in Baku mobilized and demanded the nationalist government surrender power, which they eventually did to avoid bloodshed. The Baku Bolsheviks “requested Soviet military assistance,” which arrived the next day, April 28, in the form of armored trains. That day, the Azerbaijan Soviet Socialist Republic was declared; it would not regain full independence until 1991. The new Soviet regime was not universally accepted, and there were uprisings against it that would tie down an entire Soviet army into the summer.
The Soviets were less successful in Armenia and Georgia; similar local uprisings by the Bolsheviks the next month failed, and a tentative Red Army probe into Georgia was beaten back. The Soviets were also reluctant to engage in direct conflict with the British, who still occupied Batum [Batumi] on the Black Sea coast. On May 7, the Soviets signed a treaty with Georgia’s Menshevik government, recognizing that country’s independence in exchange for Georgia’s agreement not to host White forces and to allow Georgian Bolsheviks to freely organize.
Sources include: Evan Mawdsley, The Russian Civil War